Test purchasing should be reformed so that shop staff are not treated as criminals - and to stop diligent workers being harshly penalised for being caught out by youngsters acting on Trading Standards instructions.
That is one of the key findings in a detailed report by two university professors, who argue that store staff are far more aware of the legal and moral issues surrounding sales of alcohol to under-18s than media coverage would suggest.
They praise the success of Challenge 21, saying there is evidence to suggest it has reduced attempted purchases of alcohol by children. But they warn that this may have triggered more shoplifting and proxy purchasing, meaning that drink is still finding its way into the hands of minors.
Dr Gillian Hopkinson, of Lancaster University Management School, and Dr Michael Humphreys, of Nottingham University Business School, said there should be a clearer code of practice for test purchasing, citing evidence that children were briefed to act older than they were. They also criticised the disproportionate attention that police appeared to give to test purchasing compared with in-store crimes like robbery and shoplifting, and suggested that local forces, with Trading Standards, should "take more direct responsibility in equipping store staff to implement the 21 policy".
The report was based on interviews with 48 shop staff in off-licences, convenience stores and supermarkets in the Midlands and north west England.
The report found that cashiers in general have a good working knowledge of the law and do not intentionally sell drink to children. It added that staff are not intimidated by asking for ID, and are used to abusive reactions when sales are refused.
But the authors say: "Community store cashiers feel they are on the frontline of achieving a better society. The test purchase system as it stands is seen as treating cashiers as the opposite - criminals deliberately, or at least uncaringly, selling alcohol to children.
"The test purchasing system might be more effective if it did not form the main - in some cases the only - axis of contact between the two sides."
They recommend that refusals are logged electronically and that the past performance of cashiers is taken into account if they are ever caught by test purchasing.
The report also calls for a review of the ID card system, and "the maximum possible publicity" for the Challenge 21 scheme.
But Brandon Cook, a Tradings Standards officer from Staffordshire and the Trading Standards Institute's lead officer on test purchasing issues, was unimpressed with the report. "My team of five officers spend 5 to 10 per cent of their time doing enforcement-type work," he said. "The rest of the time is split 50-50 between going out to schools and youth centres, trying to deter people from buying drink in the first place, and talking about sensible use of alcohol.
"The other half is spent visiting traders and talking to them about training, refusals books and so on. We spend a lot of time educating traders. When my staff come back in and say we got three sales I'm absolutely gutted, because I think what more can we do."